1. Field of the Invention
The present invention relates to a method for fabricating capacitors for semiconductor devices and, more particularly, to a method for fabricating capacitors that exhibit improved electrical characteristics and are capable of ensuring the capacitance levels required for advanced semiconductor device.
2. Description of the Related Art
In order to manufacture semiconductor devices having even higher degrees of integration, active research and development activities are being directed toward reducing cell area and reducing device operating voltages.
Although high degrees of integration result in greatly decreased capacitor area, the charge capacity required for proper operation of a memory device remains essentially the same. This requirement means that the capacitance for a given unit area must be increased.
Accordingly, various methods of ensuring sufficient capacitance for DRAM capacitors have been proposed. For example, methods of increasing the area of a capacitor by modifying the physical structure of the capacitor to form a three-dimensional structure such as a cylinder or reducing the thickness of a dielectric film have been used until recently.
Recently, research has also been conducted to provide a dielectric film having a NO (Nitride-Oxide) structure or an ONO (Oxide-Nitride-Oxide) structure in place of the conventional silicon oxide. Other alternative dielectric films that have been considered include Ta2O5 or BST (BaSrTiO3) that ensure a high capacitance providing an increased dielectric constant (typically 20 to 25).
However, capacitors using an NO or ONO dielectric film are generally considered inadequate for ensuring the capacitance required for next generation memories of 256 M or more. For this reason, research and development projects focussing on next generation dielectric materials, for example Ta2O5, are being pursued.
In the case of a Ta2O5 thin film, substitutional Ta atoms inevitably exist in the thin film due to composition ratio differences between Ta and O resulting from unstable stoichiometry within the thin film.
Furthermore, a reaction between the organic component of Ta(OC2H5)5, which is an organic precursor of Ta2O5, with O2 gas (or N2O gas) occurs during the formation of the Ta2O5 dielectric film, thereby producing impurities such as, carbon (C), carbon compounds (CH4 and C2H4), and water (H2O) that are incorporated into the film. As a result of the contaminants, leakage current tends to increase and the dielectric characteristics tend to be degraded in the resulting capacitor.
Although the impurities existing in the Ta2O5 thin film may be removed by conducting a low-temperature heat treatment two or three times, (for example, a plasma N2O or UV-O3 treatment) these processes can be complex and their results unreliable. Furthermore, these processes have a drawback in that they will induce oxidation of the lower electrode at its interface with the Ta2O5 thin film.
The present invention has been made in view of the above mentioned problems involved in the related prior art, and an object of the invention is to provide a method for fabricating capacitors of a semiconductor device that will improve the electrical characteristics of the resulting capacitors while ensuring a level of capacitance required in the semiconductor device.
Another object of the invention is to provide a method for fabricating capacitors for semiconductor devices, that will tend to remove impurities, from a dielectric film, that would generate leakage currents, thereby forming a high quality dielectric film.
Another object of the invention is to provide a method for fabricating capacitors for semiconductor devices, that can eliminate prior art processes necessary to increase the surface area of a lower electrode in order to ensure sufficiently high capacitance, thereby simultaneously reducing the number of unit processing steps, the processing time, and the manufacturing costs.
In accordance with one embodiment, the present invention provides a method for fabricating capacitors for semiconductor devices, comprising the steps of: forming a lower electrode on a semiconductor substrate; forming an amorphous TaON thin film over the lower electrode, annealing the deposited amorphous TaON thin film in an NH3 atmosphere, forming a second amorphous TaON thin film and the annealing the amorphous TaON thin film at least once more, thereby forming a TaON dielectric film having a multi-layer structure; and forming an upper electrode over the TaON dielectric film.
In accordance with another embodiment, the present invention provides a method for fabricating capacitors for semiconductor devices, comprising the steps of: forming a lower electrode on of a semiconductor substrate; forming an amorphous TaON thin film over the lower electrode, annealing the amorphous TaON thin film in an NH3 atmosphere, forming a second amorphous TaON thin film and annealing the amorphous TaON thin film twice, thereby forming a TaON dielectric film having a multi-layer structure; and forming an upper electrode over the TaON dielectric film.
In accordance with another embodiment, the present invention provides a method for fabricating capacitors for semiconductor devices, comprising the steps of: forming a lower electrode on of a semiconductor substrate; nitriding an upper surface of the lower electrode in an NH3 atmosphere; forming an amorphous TaON thin film over the lower electrode, annealing the amorphous TaON thin film in an NH3 atmosphere, forming a second amorphous TaON thin film and annealing the amorphous TaON thin film at least once more, thereby forming a TaON dielectric film having a multi-layer structure; and forming an upper electrode over the TaON dielectric film.